In physics class, the girl to boy ratio is $5$ to $6$. If there are $20$ girls, how many boys are there?
A ratio of $5$ girls to $6$ boys means that there is a group of $5$ girls for every group of $6$ boys. If there are $20$ girls, then there are $4$ groups of $5$ girls each. Because we know the ratio is $5:6$ , there must be $4$ groups of $6$ boys each. There is a total of $24$ boys in physics class.